Cold cathode discharge tube



March 5, 1935. H. J. sPANNER Er AL.

COLD CATHODE DISCHARGE TUBE Filed OCT.. 2l, 1929 INVENTORS Hans JSpan/zer Zwin/17d" Jer/nef BY Anm/ 6m @ve ATTORNEYS Patented-Mar. 5,1935 I UNITED STATES PATENT oFFlcE Germany, poration of Delawareassignors to Electrons, Inc., a cor- Application October Z1, 1929,Serial No. 401,110 In Germany May 4, 1929 8 Claims.

This invention relates to discharge tubes generally and moreparticularly to rectiers employing electron emissive cathodes of theso-called cold type.

The object of this invention is to provide an improved electron emissivebody which is particularly adapted for employment as a cold cathode inan alternating current rectier or other discharge tube; in other words,an electrode which will have ample emissivity at low current and lowtemperature, and which shall, in addition, when properly incorporated inthe rectifier, have a very small voltage drop, have long emissive life,and be enabled to carry relatively high current loads.

As corollary to this invention, it is also our object to provide arectifier having high eciency and economy, particularly one which shallnot require a separate heating element, such as a heating coil orspiral, or transformer winding, in order to secure the necessarytemperature to bring the cathode body to an emissive state.

We have found quite generally that an electrode having a core of aneutral or inert metal, such as nickel or iron, specially activated,coated or treated with an admixture of a highly emissive orelectropositive substance, such as barium or csium and a poorlyconducting ternary compound consisting of an element or cation ofmoderately electropositive character and a complex anion which compoundis not surllciently acidic to impede or interfere with electronemission, such as magnesium cuprate, csium tungstate or strontiumzirconate, or the like, has the desirable properties described above,namely that when employed as a cathode it requires no separate heatingelement to bring the temperature thereof to a point high enough Where itwill emit electrons, but will emit at very low temperatures of the coreand by the application of relatively very small discharge current'bycreating hot spots on the coating which become larger with increasingcurrent. i

At the same time, it will be found that the life of such an electrode isvery long, iirst, because there can be, of course, no appreciableevaporation where low temperatures are employed, and secondly, becausethe compounds We have chosen as part of the special activation materialare not susceptible to disintegration or dissociation by ionicbombardment under operating conditions and because too, these compoundshave a common characteristic that they have relatively high vaporizationpoints.

When employing this electrode as a cathode (Cl. Z50-27.5)

in the rectier, we nd it advisable and desirable that the rectifier tubecontain an inert gas, such as argon, or neon, at a pressure, for argon,of about 1.8 mm., and for neon of about mm. As a matter of fact, thesegas pressures are rather critical for the most efcient performance ofthe tube. and it is well to have present also in the tube a littlemercury, caesium or other suitable metallic vapor.

And as anode, We prefer to use an electrode composed of a substance suchas iron tungsten or carbon.

In our preferred embodiment the cathode comprises a strip of intermeshednickel wires treatedA or coated in any well-known manner with thespecial activation substance above described, either before or afterensealing into the tube. A suitable cathode would be one coated ortreated with an admixture of barium and csium tungstate, for example,and shaped into a hollow body and therein would be inserted two anodesor more, one at least of which is spaced apart from the cathode about 3mm.

However, our cathode may be made of such small proportions that it maybe placed between or surrounded by a plurality of anodes. The anodes maybe cylindrical in form with the cathode disposed therebetween.

In the event small cathodes are used, we prefer to shape the anode oranodes in the form of hollow bodies into which we put screens so thatthe discharge shall follow a fixed path, depending on the potential atthe electrode at that time and also that the discharge may not come incontact with the glass wall of the tube, if possible. As a screen, wemay use electron clouds, that is, cathode rays. But we may rely upon themirror formed by the getter metal to keep the discharge from the glass.

In the accompanying drawing which forms part of this specification Fig.1 illustrates one embodiment of our invention;

Fig. 2 is a cross-section, on line 2-2, of the tube shown in Fig. 1, toa smaller scale;

Fig. 3 illustrates another embodiment of our invention.

In Fig. 1 the envelope of an electron discharge device or tube isindicated by reference character 1 and contains a cathode 2 ofintermeshed wires having the previously described special activatingsubstances applied thereto, and cylindrical anodes 3 and 4 disposed onopposite sides of the cathode. The electrodes may be supported above apress and provided with conducting leads in the usual manner. Since onlyone cathode lead is necessary in operation as a "cold" cathode, theleads to the cathode 2 may be connected together.

It should be understood that envelope 1 may be provided with a gasfilling, such as one or more of the inert gases, and may also contain asmall quantity of an easily vaporizable metal, for example mercury, orcsium, as indicated Vat 8. In the case of csium and other highlyelectropositive metals, the metal when vaporized may condense in thetube in the form of a thin coating on the inner wall and otherrelatively cool parts thereof. The gas filling or metal vapor or amixture of both provides anionizable atmosphere fo the tube. I f I Fig.2 is a cross-section of the tube shown in Fig. 1 looking downward uponthe electrodes and shows their relative positions.

Fig. 3 illustrates an' embodiment of the invention containing a cathode5 similar to cathode 2 of Fig. 1 but having a plurality of anodes 6 eachof which is shaped to form a portion of a cylindrical surface, theanodes taken together forming a substantially cylindrical enclosure forcathode 5. The screens above mentioned may be inserted as shown at 7.

It should be understood however, that the embodiments shown anddescribed herein are merely illustrative and that our invention isnotlimited to a particular shape of cathode or to a particulararrangement of electrodes.

The operation of our tubes is as follows: When the current source havinga difference of potential, say of 100 volts, is applied to theelectrodes there appears a blue discharge such as is noticeable in theordinary form of glow lamps. This discharge, then takesan entirelydifferent and more intense form, and electrons are given off exactly asfrom the` heated cathode. An explanation of this rapid building up ofthe electron ow and profuse emission is that after the'initial orstarting impulse therev occurs automatically a sort oi mutually boostinginteraction between glow discharge and electron emissiomthat is, the'initially emitted electrons create, a glow discharge. This glowdischarge causes atndncr'eased electron emission.. Theincreasedelectronjfemission produces an increased glow discharge, and soon, until a'vast electron flow is`/established limited only by the pointof saturation, and we believe that'this building up is due to theagitation or stimulation of the special activation material by the glowcurrent.

In the appended claims we have used the word coating as synonymous withactivated or treated and where one is used the others may be substitutedas being comprehended by' the disclosure; that is, where we say"a corecoated with a mixture etc., it may be read as a core activated wit or acore treated with etc.

In a rectifier made in accordance with the above instructions, it willbe found that the cathode voltage drop is very low, and thatvaporization of the electron emissive material is negligible, and thatthe rectier is capable of handling unusually high current loads withunusually high curren output.

It will be observed that the ternary compounds of our special activationmaterials belong to a cation, but less electronegative than the oxygen.

It will be understood that the size of the electrodes, as well as otherfactors, will depend upon current load which the rect'iiler will berequired to handle.

And though we have disclosed specific adaptations and embodiments loitour inventionwe are not to be understood as limiting in any way thescope of the invention since it is conceivable that it may be applied toand adapted for discharge tubes of forms and for piu'poses other thanthat of and for a rectifier.

Having described our invention, what we claim is:

1. An electron emitting cathode, and an electron emissive coatingthereon, the said coating comprising a mixture of a highly emissivesubstance and magnesium cuprate.

2. An electron emitting cathode, and an electron emissive coatingthereon, the said coating comprising a mixture of a highly emissivesubstance and-csium tungstate.

3. An electron emitting cathode comprising a -core of metal of the irongroup in the form of intermeshed wires, and an electron emissivecoatingthereon, the said coating comprising a highly electron emissivesubstance and magnesium cuprate.

4. An electron emitting cathode comprising a core of metal of the irongroup in the form of intermeshed wires, and an electron emissive coatingthereon, the said coating comprising a highly electron emissivesubstance' and csium tungstate.

5. An electron discharge device comprising an anode, a cathode having ametallic core the surface of which is activated with a highlyelectropositive metal, a coating of a ternary compound on said surfacewhich is substantially non- .emissive and resistive to ionicYbombardment,

said compound consisting of a metal of the alkaline group, a lesselectropositive metal and oxygen, and an ionizable atmosphere in saiddevice containing vapor of the activating metal.

v6. An electron discharge device comprising an anode, a cathode, and anionizable atmosphere containing a rare gas and csium', said cathodehaving a core activated with csium and a coating of cslum tungstatethereon.

7. A cathode adapted to be rendered emissive by ionic bombardmentcomprising a core activated with a metal of the alkaline group and acoating thereon comprising a compound of a highly electropositive metaland the Oxy-acid radical of a more electronegative metal, said compoundbeing highly resistive to dissociation and disintegration by ionicbombardment and the degree of acidity of which is insuiiicient tointerfere with the electron emission of the activated core.

8. An electron discharge device comprising an anode, a cathode having ametallic core activated with a highly electropositive metal, a coatingof a ternary compound on said core which is substantially non-emissiveand resistive to ionic bombardment, said compound consisting of a metalof the alkaline group, a less electropositive metal and oxygen, and anionizable atmosphere in said device containing argon at a pressure ofabout 1.8 mm. of mercury and metal vapor.

J HANS J. SPANNER.

EDMUND GERMER.

